Sunday, September 28, 2014

Green is Good: Slaying the Uber Mega-Sauropod

So I noticed I have not written much about plants lately but have been instead looking at marine reptiles and of course Spinosaurus in recent months - and thats ok (its my blog after all and expect MUCH more on Spinosauridae in the future). However I have been watching my feed and noticing a lot of hits coming in from various dino chat boards/ "dino fanboy" sites/ reddit etc. etc. - probably a lot to do with my Spinosaurus posts.  And this concerns me a bit in that I don't want this blog to turn into Carnivora forum type of place - but if you are from one of the JP forums/ Carnivora forums please stick around and hopefully I can convert you to a more egalitarian view of the past. So as an antidote to this concerning trend I am going to talk about plants (and at the end maybe a word or two about dinosaurs). 'Cause nothing should scare dino fanboys away more than talk about boring ol' plants, am I right? People coming in from DeviantArt you guys are cool, open-minded, and generally not of the same ilk please stay around. 

I want to post some pics of the Norfolk Island Pines (Araucaria heterophylla) in my backyard. And if you don't know why trees like this are important in Mesozoic paleoecology GTFO.  The cones these guys produce are pretty neat looking and just recently have started going to seed. They take a LOOOOONG time to mature. Wikipedia said they take 18 months to mature but I have pictures of these same cones from at least January of 2013 so that number from wiki may in fact be at the low end.

Same tree with cones coming in Jan 2013
Now I have seen an invasive Fox squirrel (Sciurius niger) rampaging about in my backyard for several months and although I have yet to see it in this tree I would not put it past a known predator of pine seeds to pillage these guys. There is a tasty and nutritious seed inside the woody, protective husk. Humans themselves will feast on the seed of related species. And I have seen ravens dropping kernels from a large Bunya-Bunya pine in the path of oncoming vehicles to crack the husk so that they can get at the tasty kernel. Students of Mesozoic life should not miss the potential for beaked ornithopods, stout jawed sphenodonts, various proto-aves, and multiberculates to have behaved in a like-wise manner.

Araucariaceae occurred throughout the Mesozoic and there is much to suggest that the family has changed very little. In the book Plants in Mesozoic Time Ch-5 Carole T. Gee and William D. Tidwell document the preserved whole plant remains of Araucaria delevoryassi from the Howe-Stephens Quarry of the famed Morrison Formation (i.e. big sauropod country). As you noticed they placed it in the same genera as modern species of araucariaceae and noted a suite of characters suggesting a mosaic of primitive and advanced features in it. Digestibility tests suggest the foliage of these trees offered an abundant and nutritious option for sauropods provided that they digested it for long enough periods of time.

I think that this is a reasonable option, especially for high-browsing sauropods. What I find interesting and a bit of a conundrum is that modern members of Araucariaceae are not particularly fast growers. Now one can make the argument that with their main predators - the sauropods - long extinct modern members of this family have divested from fast growth rates but I personally don't find this argument compelling. Why lose the fast growth rate if you ever had it to begin with? I have experimented with trimming some branches off of a larger A. heterophylla in my backyard. New growth will sprout out from the where the old branch was snipped off, but often from several latent nodes creating a bushier effect.

Artists of Mesozoic foliage striving to show how sauropod modified araucariaceae trees look should take note - what was once one branch has, after pruning, turned into a much more bushier "shelved" habit of several branches for the tree. What should be noted is that this modest growth - occurred over several years since I initially pruned it - not a spectacularly high rate of re-growth from pruning. If Mesozoic araucaria trees had similar growth speeds, and I find no compelling reason that they should not, this suggests to me that heavy sauropod browsing was mitigated to an extent by  predators/parasites/water needs necessitating constant nomadic movements as not to put their primary food source in a negative carbon balance.

Images like this, depicting sauropod herds ravaging the landscape, toppling trees, and devouring ad infinitum should be balanced with a more nuanced view of sauropod (and other dino megaherbivores) and plant coexistence. Admittedly I am arguing the negative a bit here. Of course sauropods (and other megaherbivorous dinos) toppled trees, disrupted/compacted roots systems, and plowed paths through the vegetation. Of course these things happened - it was just a matter of course for such large animals. But what I fear is happening is that we are seeing a parallel to the hypercarnivorous, all consuming semi-mythologized uber-theropod of recent years, except this time happening with megaherbivorous dinosaurs. Large sauropods and other dino megaherbivores may have just as well fostered diversity and heterogeneous patches in their landscape, huge piles of feces may have acted as recruitment sites for young plants - especially via seeds and spores that passed undigested through their digestive tract - and consumption of faster growing species allowing slower growing species to thrive. Large sauropods and other megaherbivorous dinosaurs may have in fact fostered and benefited the exact plant community that they depended on for food.

In fact a recent paper may provide some insight and suggest a much more nuanced relationship of herbivorous dinosaurs to the plant communities that they fed upon.  Plant Ecological Strategies Shift Across the Paleogene-Cretaceous Boundary. What this paper suggests is that the angiosperm plant regime shifted from a relatively slow growing, evergreen dominated strategy in the Cretaceous to a faster growing/higher vein density regime of deciduous angiosperms after the K-Pg event. This ecological reset would have selected against the slower growing angiosperms and shifted the balance towards the metabolically faster deciduous plant community we see today. And here it should be reinforced that this changing of the guards occurred over a relatively short span of time of less than two million years. The faster growing species were around during the Cretaceous yet it took the meteor impact to provide the disruption that gave them the toe hold that they needed. And keep in mind that during the Cretaceous the slow growing angiosperm community - itself making inroads on the even slower growing gymnosperm/pteridophyte community that dominated most of the Mesozoic - existed under the auspices of supposedly some of the most disruptive/all consuming/omnipotent herbivorous animals the world has ever seen - dinosaurian megaherbivores. But if megaherbivorous dinosaurs were so aggressive/all consuming/disruptive why did they themselves not shift the angiosperm regime to a more quickly growing regime and not the K-Pg event? For me this is very suggestive and opens up many other questions. Were dinosaurs themselves keeping the faster growing species at bay and thus allowing  slower growing species to proliferate? And, if true, then perhaps it was the extinction of the dinosaurs that allowed the faster growing species to proliferate after the extinction of their chief predators? Or did herbivorous dinosaurs not matter at all to large trends in plant evolution and climate change/evolutionary innovation/ and extinction events are really what matter?

Kenneth Lacovara Phd, Dreadnoughtus remains
And one final word on megaherbivorous dinosaurs. We were recently treated to the rollout of the most complete and well preserved mega-sauropod ever recovered Dreadnoughtus schrani. Of course I am a little late to the game on covering this guy but - you know it is over 65 million years old so I think time is relative... But to my point of being careful not mythologize megaherbivorous dinosaurus the same way we do to mega-theropods:

“With a body the size of a house, the weight of a herd of elephants, and a weaponized tail, Dreadnoughtus would have feared nothing,” Lacovara said. “That evokes to me a class of turn-of-the-last century battleships called the dreadnoughts, which were huge, thickly clad and virtually impervious.” 

My critique is aimed at the very name of the beast - implied to "fear nothing". To me the idea of an animal that fears nothing speaks to a very maladaptive trait. A dinosaur this size should still fear lots of things. It should fear crossing uneven ground and breaking a leg. It should fear getting mired in mud. It should fear other members of its own species that might fight it for mates, water, or food. It should fear too high a parasite load. And as I will explain in a second it should still fear theropods even if it had grown out of the ontogenetic stage where it fell in the range of prey.

One of my favorite bits from Greg Paul's Princeton Field Guide to Dinosaurs was where he mused on the challenges that a field expedition of humans into the Mesozoic would face:

"A herd of whale-sized sauropods would pose a serious danger of trampling or impact from their tails, especially if they were spooked by humans and either attacked them as a possible threat or stampeded in their direction. Sauropods would certainly be more dangerous than elephants, whose high level of intelligence allows them to better handle situations involving humans." GSP

And here I think it important to recognize that anger and aggression - in animals and humans - is often the result of fear itself. If an animal is truly without fear then it would not even bother with acting aggressive - such as stamping the life out of a theropod. And mega-sauropods, perhaps surviving several dozen theropod attacks over the course of their lives before attaining a size range putting them out of threat, had evolutionary impetus to fear theropods. And when achieving a size outside the prey range of theropods who is to say that they were even intelligent enough to recognize this fact? Many animals, including humans, have been suggested to have predator recognition hardwired into their brain. Again sauropods - having to grow through several different size classes - would have been vulnerable to theropods for much of their life. Their would be evolutionary impetus for these animals to have a built in hardwired innate fear of theropods. And with the conservative theropod bauplan and long evolutionary history between the two groups there is much space and time for sauropods to evolve an innate predator recognition of theropods. So images of sauropods crushing the life out of theropods are just as plausible as huge adult sauropods getting spooked and fleeing away from harmless, small theropods.

Even relatively big-brained mammals such as the deer in this video display latent fear of house cats arguably due to predator recognition. I would suspect smaller brained sauropods (and other dinos) acted  with much the same consternation, confusion, and stress when faced with a theropod. How they react - either fleeing or attacking is besides the point. It was fear that caused the reaction. And it was this perpetual "landscape of fear" that theropods maintained - whether or not they could even attack/prey upon the animal - that mitigated wholesale destruction/over browsing of Mesozoic plant communities.

Or you may disagree.

Support me on Patreon.
Like antediluvian salad on facebook.
Watch me on Deviantart @NashD1.Subscribe to my youtube channel Duane Nash.


Anonymous said...

I can understand how the "climate of fear" would keep herbivorous dinosaurs on the move and keep their numbers down to the point that they didn't make any impact on plant communities. But how would these dinosaurs keep the faster growing angiosperm species at bay? Would they only eat the faster growing species, and not the slower ones, and thus keep them from becoming dominant? Or was it something else?

Duane Nash said...

I am not saying they did not make an impact, only that the impact might be a bit overstated and might be a bit more nuanced than traditionally depicted. Facultative effects of large herbivores for instance; game trails creating fire breaks; large dung piles serving as recruitment sites for seeds and spores; break down of woody material. These and other factors are commonly observed today and although direct evidence of these interactions may be lacking they can to some extent be reasonably inferred.

Duane Nash said...

And with regards to your question "how could these dinosaurs keep the faster growing angiosperm species at bay?" yes if they constantly pruned back aggressive fast growing species that is a reasonable hypothesis. But things were complicated. Invertebrates and small vertebrates played roles - maybe substantial - as well.

Also keep in mind non-angiosperms can be fast growing and invasive as well - azolla water ferns, horestails, and climbing ferns like Lygodium come to mind.

If can paint with a broad stroke this is how I imagine it working. Large herbivores through their consumption and landscape engineering providing opportunities for slower growing plants, seedlings, and smaller animals to gain footholds/habitat. Browsing hard but not to the point of an impoverished landscape in terms of diversity of species and vegetative cover. Predators, water needs, and parasite burden keeping them always a little bit on the move.

Again don't go away reading this post and thinking I am 100% right - we might never get any direct evidence for these ecological processes. But with what we have and with how we can roughly approximate from living large herbivores and their ecologies this >is how I imagine it<.

But yes trimming back of fast growing species is a way to allow slower growing ones to get a good toehold. That is what gardeners have to do all the time so that the ivy. vines, trailing roses etc etc don't crowd out the slower growing plants. Replace a weed-whacker or hedge trimmer with an iguanodont or a titanosaur and you get the gist of the argument.

I am also planning a post on how fire may have played a role in all of this in the future.

thanks for comment and please consider writing down a name in the future.

Related Posts Plugin for WordPress, Blogger...